Remote storage disk control device and method for controlling the same

ABSTRACT

A storage device system includes an information processing device, a first storage device equipped with a first storage volume, and a second storage device equipped with a second storage volume. The information processing device and the first storage device are communicatively connected to one another. Also, the first storage device and the second storage device are communicatively connected to one another. The information processing device is equipped with a first write request section that requests to write data in the first storage device according to a first communications protocol, and a second write request section that requests to write data in the second storage device according to a second communications protocol. The information processing device creates first data including a first instruction to be executed in the second storage device.

CROSS REFERENCES

This is a continuation application of Ser. No. 12/071,325, filed Feb.20, 2008 (now U.S. Pat. No. 7,707,377), which is a continuationapplication of Ser. No. 11/492,892, filed Jul. 26, 2006 (now U.S. Pat.No. 7,363,461, which is continuation of application Ser. No. 11/087,983,filed Mar. 22, 2005 (now U.S. Pat. No. 7,165,163), which is acontinuation of Ser. No. 10/748,886, filed Dec. 30, 2003 (now U.S. Pat.No. 7,219,201).

This application claims priority to JP 2003-325082 filed Sep. 17, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling a storagedevice system, a storage device system, and a storage device.

2. Related Background Art

Disaster recovery in information processing systems is attractingattention. As a technology to realize such disaster recovery, atechnology in which a copy of data stored in a storage device that isinstalled in a primary site is also managed by a storage device that isinstalled in a remote site located away from the primary site is known.By using the data stored in the storage device installed at the remotesite when the primary site is hit by a disaster, processings that areperformed at the primary site can be continued at the remote site.

For data transfer from the primary site to the remote site, a method inwhich data is exchanged between an information processing device at theprimary site and an information processing device at the remote site isknown. The information processing device at the primary site transfers acopy of data that is written in the storage device at the primary siteto the information processing device at the remote site. The informationprocessing device at the remote site that has received the copy of datasends a request to write the data in the storage device at the remotesite.

When data is stored as a backup by the method described above, asubstantially large amount of data flow occurs on the network betweenthe information processing devices. This causes a variety of problemssuch as an increased interface processing load on the informationprocessing devices, delays in other data transmissions to be conductedbetween the information processing devices, and the like. Also, themethod described above needs software to control data backup to beinstalled in each of the information processing devices. For thisreason, management works such as upgrading the software and the likeneed to be performed on all of the information processing devices thatexecute data backup processings, which increases the management cost.

SUMMARY OF THE INVENTION

The present invention has been made in view of the problems describedabove, and relates to a storage device system, a storage device and amethod for controlling a storage device system.

In accordance with an embodiment of the present invention, there isprovided a method for controlling a storage device system that includesat least one information processing device, a first storage deviceequipped with a first storage volume, and a second storage deviceequipped with a second storage volume, wherein the informationprocessing device and the first storage device are communicativelyconnected to one another, the first storage device and the secondstorage device are communicatively connected to one another, theinformation processing device is equipped with a first write requestsection that requests to write data in the first storage deviceaccording to a first communications protocol, and the first storagedevice is equipped with a second write request section that requests towrite data in the second storage device according to a secondcommunications protocol. The method comprises: a step in which theinformation processing device sets a first instruction to be executed atthe second storage device as first data; a step in which the informationprocessing device sends a request to write the first data in the firststorage volume to the first write request section; a step in which, whenthe first data written in the first storage volume is an instruction tothe second storage device, the first storage device sends a request towrite the first data in the second storage volume to the second writerequest section; and a step in which the second storage device executesthe first instruction that is set as the first data written in thesecond storage volume.

It is noted that the information processing device may be, for example,a personal computer, a work station or a mainframe computer. The storagedevice may be, for example, a disk array device or a semiconductorstorage device. The storage volume may be a storage resource thatincludes a physical volume that is a physical storage region provided bya disk drive, and a logical volume that is a storage region logicallyset on the physical volume. Also, the communications protocol may be,for example, a WRITE command stipulated by a SCSI (Small Computer SystemInterface) standard. As a result, without adding new commands to theoperating system, the information processing device can make the secondstorage device to execute the first command.

Here, for example, when the first command is a command to read data ofthe first storage device, the second storage device can have a copy ofthe data of the first storage device according to an instruction fromthe information processing device. Therefore the present method canreduce the amount of data communicated between the informationprocessing devices in the data backup management. Also, software forcontrolling data backup does not have to be installed on all of theinformation processing devices that are performing data backup, whichlowers the management costs.

Other features and advantages of the invention will be apparent from thefollowing detailed description, taken in conjunction with theaccompanying drawings that illustrate, by way of example, variousfeatures of embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a system configuration of an informationprocessing system in accordance with an embodiment of the presentinvention.

FIG. 2 schematically shows a structure of a disk array device inaccordance with an embodiment of the present invention.

FIG. 3 shows a LUN map information table in accordance with anembodiment of the present invention.

FIG. 4 schematically shows a diagram illustrating a data writingoperation using virtual volumes in accordance with an embodiment of thepresent invention.

FIG. 5 shows a command device management table in accordance with anembodiment of the present invention.

FIG. 6 shows a command device interface in accordance with an embodimentof the present invention.

FIG. 7 is a schematic diagram illustrating execution of commands set atcommand devices in accordance with an embodiment of the presentinvention.

FIG. 8 shows a flowchart of an operation to control a command device inan information processing device in accordance with an embodiment of thepresent invention.

FIG. 9 shows a flowchart of an operation to control a command device ina storage device in accordance with an embodiment of the presentinvention.

FIG. 10 shows a pair management table in accordance with an embodimentof the present invention.

FIG. 11 shows a schematic diagram illustrating a pair forming processingin accordance with an embodiment of the present invention.

FIG. 12 shows a relation between a primary volume and a primary journalin accordance with an embodiment of the present invention.

FIG. 13 is a schematic diagram illustrating a journal acquisitionprocessing in accordance with an embodiment of the present invention.

FIG. 14 is a schematic diagram illustrating a restoration processing inaccordance with an embodiment of the present invention.

FIG. 15 shows journal data regions of a primary journal and an auxiliaryjournal in accordance with an embodiment of the present invention.

FIG. 16 shows a flowchart of a journal acquisition processing and arestore processing performed in information processing devices inaccordance with an embodiment of the present invention.

FIG. 17 is a schematic diagram illustrating a swap processing inaccordance with an embodiment of the present invention.

FIG. 18 is a schematic diagram illustrating a state in which the swapprocessing of the present embodiment is completed.

FIG. 19 shows a flowchart of a swap processing in a second informationprocessing device in accordance with an embodiment of the presentinvention.

FIG. 20 shows a flowchart of a swap processing in a first storage devicein accordance with an embodiment of the present invention.

FIG. 21 shows a flow chart of a swap processing in a second storagedevice in accordance with an embodiment of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

[Example of Overall Structure]

FIG. 1 schematically shows an overall structure of an informationprocessing system including a storage device system in accordance withan embodiment of the present invention. The information processingsystem of the present embodiment includes an information processingdevice 11, and at least a first storage device 10 and a second storagedevice 20. The first storage device 10 is equipped with a logicalvolume(s) 30 on which the first storage device performs datainput/output processings (hereafter referred to as a “first logicalvolume(s)”), and the second storage device 20 is equipped with a logicalvolume(s) 40 on which the second storage device performs datainput/output processings (hereafter referred to as a “second logicalvolume(s)”).

The information processing device 11 and the first storage device 10 arecommunicatively connected to each other via a first network 50. Thefirst network 50 may be, for example, a LAN (Local Area Network), a SAN(Storage Area Network), an iSCSI (Internet Small Computer SystemInterface), an ESCON (Enterprise Systems Connection)®, or a FICON (FibreConnection)®.

The first storage device 10 and the second storage device 20 arecommunicatively connected to each other via a second network 60. Thesecond network 60 may be, for example, a Gigabit Ether Net®, an ATM(Asynchronous Transfer Mode), or a public telephone line.

[Information Processing Device]

The information processing device 11 may be a computer that is equippedwith a CPU (Central Processing Unit), memories, and other devices. Theinformation processing device 11 may be a personal computer, a workstation or a mainframe computer. The information processing device 11may be composed of a plurality of computers that are mutually connected.An operating system is operating on the information processing device11, and application software is operating on the operating system.

[Storage Device]

FIG. 2 shows a structure of a disk array device, which is described asan example of the first storage device 10 and the second storage system20. Instead to of the disk array device, the first and second storagedevices 10 and 20 may be any appropriate devices, such as, for example,semiconductor storage devices. For example, the disk array device 10 isequipped with various components including a channel control section201, a remote communications interface 202, disk control sections 203, ashared memory 204, a cache memory 205, a switching control section 206that is composed of cross bus switches that communicatively connect thecomponents described above, a management terminal 207, and memorydevices 208. The first and second storage devices 10 and 20 may have thesame structure.

The cache memory 205 is used to temporarily store data that is exchangedmainly between the channel control section 201 and the disk controlsections 203. For example, when a data input/output command which thechannel control section 201 receives from the information processingdevice 11 is a write command, the channel control section 201 writes inthe cache memory 205 write data received from the information processingdevice 11. Also, an appropriate one of the disk control devices 203reads the data written in the cache memory 205, and writes the same inthe memory devices 208.

The disk control section 203 reads a data I/O request stored in theshared memory 204 written by the channel control section 201, andexecutes data writing processing or data reading processing with respectto the memory devices 208 according to a command set at the data I/Orequest (for example, a command according to a SCSI standard). The diskto control section 203 writes in the cache memory 205 data that has beenread out from the memory devices 208. Also, the disk control section 203transmits to the channel control section 201 notifications, such as, forexample, a data write completion notification and a data read completionnotification. The disk control section 203 may be equipped with afunction to control the memory devices 208 with RAID levels (forexample, 0, 1, 5) stipulated in the so-called RAID (Redundant Array ofInexpensive Disks) method.

The memory devices 208 may be, for example, hard disk devices. Thememory devices 208 may be provided in one piece with or separately asindependent devices from the disk array device. Storage regions providedby the memory devices 208 at each site are managed in units of logicalvolumes 209, which are volumes that are logically set on the storageregions. Data can be written in or read from the memory devices 208 bydesignating LUNs (Logical Unit Numbers) that are identifiers appended tothe corresponding logical volumes 209. Also, the logical volumes 209 aremanaged in units of a predetermined data amount such as units of 512 Kb,such that input and output of data in this predetermined unit areconducted. Each of the units is called a logical block, and each of thelogical blocks is appended with a logical block address (hereafterreferred to as a “LBA”) that indicates positional information of thelogical block.

The management terminal 207 may be a computer for maintaining andmanaging the disk array device and the memory devices 208. Changes inthe software and parameters to be executed by the channel controlsection 201 and the disk control section 203 can be conducted by givinginstructions from the management terminal 207. The management terminal207 can be in a form that is built in the disk array device, or can beprovided independently from the disk array device.

The remote communications interface 202 is a communications interface(i.e., a channel extender) that is used for data transfer to anotherstorage device. A copy of data is transferred in a remote copy operationto be descried below through this remote communications interface 202.The remote communications interface 202 converts the interface of thechannel control section 201 (for example, an interface such as an ESCONinterface or a FICON® interface) to a communications method of thesecond network 60, whereby data transfer with the other storage devicecan be realized.

Besides the structure described above, the disk array device may have astructure that functions as a NAS (Network Attached Storage) configuredto accept data input/output requests through designating file names fromthe information processing device 11 according to a relevant protocolsuch as a NFS (Network File System).

The shared memory 204 can be accessed from both of the channel controlsection 201 and the disk control section 203. The shared memory 204 isused for delivering data input/output request commands, as well as forstoring management information for the storage devices 10 and 20, andthe memory devices 208. In the present embodiment, the shared memory to204 stores a LUN map information table 301 shown in FIG. 3, a commanddevice management table 501 shown in FIG. 5, and a pair management table1001 shown in FIG. 10.

[Virtual Volume]

As described above, the logical volumes 209 are storage regions that arelogically set on the physical volumes. Also, by using “virtual volumes”as logical volumes, the storage devices 10 and 20 on which the logicalvolumes 209 are set can be differentiated from other storage devicesthat are equipped with physical volumes correlated with the logicalvolumes 209.

To realize this function, the first storage device 10 stores a LUN mapinformation table 301 shown in FIG. 3. The LUN map information table 301describes information relating to the logical volumes 209 that arehandled by the first storage device 10. For example, in the presentembodiment, the LUN map information table 301 includes entries of “LUN,”“Target” and “Mapping LUN.”

Each entry at “LUN” describes a LUN for each of the logical volumes.When a logical volume 209 is a virtual volume, a storage device that isequipped with the logical volume 209 correlated with the virtual volumeis set at “Target.” Furthermore, a LUN of the logical volume 209correlated with the virtual volume is set at “Mapping LUN.” In otherwords, when there is a description at “Mapping LUN,” it means that thecorresponding logical volume is a virtual volume.

Details of the LUN map information table 301 may be registered, forexample, by an operator through the management terminal 207 that isconnected to the first storage device 10.

The first storage device 10 uses the LUN map information table 301described above and provides the second logical volume 40 of the secondstorage device 20 to the information processing device 11 by a mechanismto be described below as if the second logical volume 40 were the firstlogical volume 30 of the storage device 10. In other words, theinformation processing device 11 can make data input/output requests,which are to be issued to the logical volume 209 of the second storagedevice 20, to the first storage device 10.

Processings by the storage device system, which take place when a datainput/output request transmitted from the information processing device11 is a data write request, will be described with reference to FIG. 4.

The information processing device 11 is equipped with a first writerequest section 401 that writes data in the first storage device 10according to a first communications protocol. Upon receiving a datawrite request from the first write request section 401 (S401), the firststorage device 10 writes in the cache memory 205 data to be written thathas been received with the data write request.

A data transfer section 402 of the first storage device 10 refers to theLUN map information table 301, and confirms as to whether or not amapping LUN is set for a first logical volume 30 that is set in the datawrite request. If a second logical volume 40 is set as the mapping LUN,to the data transfer section 402 transfers to a second write requestsection 403 a request to write the data in the second logical volume 40according to a second communications protocol. In this embodiment, thesecond write request section 403 makes data write requests to the secondstorage device 20 according to the second communications protocol. Thesecond storage device 20 receives the data write request from the secondwrite request section 403, and writes the data in the second logicalvolume 40 (S402).

It is noted that the first communications protocol and the secondcommunications protocol are for example WRITE commands stipulated by aSCSI standard. Accordingly, the data write interfaces at the firststorage device 10 and the second storage device 20 do not need to bechanged.

The write processing has been so far described. It is noted however thata read processing to read data from a logical volume is also performedin a manner similar to the write processing except that data istransferred in an opposite direction with respect to the data transferdirection in the write processing.

As describe above, in the storage device system in accordance with thepresent embodiment, the information processing device 11 accesses thesecond logical volume as if the second logical volume were a logicalvolume on the first storage device 10.

[Command Device]

Each of the storage devices 10 and 20 is equipped with a “commanddevice” for controlling special commands. The command device is used toconvey commands from the information processing device 11 to the storagedevices 10 and 20, and the storage devices 10 and 20 can executecommands that are stored in the command devices. What makes the specialcommands different from ordinary commands is that the command devicesare the logical volumes 209. Functions of the command device will bedescribed below.

FIG. 5 shows a command device management table 501 that is stored ineach of the storage devices 10 and 20. The command device managementtable 501 contains entries such as “Device” and “Command Device LUN.”Entries at “Device” indicate as to which of the storage devices 10 and20 correspond to which of the command devices. Each entry at “CommandDevice LUN” sets a LUN of each logical volume 209 which expresses theentity of the corresponding command device.

Details of the command device management table 501 may be registered,for example, by an operator through the management terminal 207 that isconnected to each of the storage devices 10 and 20.

The command device management table 501 of each of the storage devices10 and 20 can register command devices of other storage devices (thatmay be similar to the storage device 10 or 20). When the command devicesof the other storage devices are registered, LUNs of virtual volumes,which correspond to the LUNs of the command devices of the other storagedevices are registered at the entries “Command Device to LUN.”

FIG. 6 shows an example of a command device interface 601, which is adata format of data that is written in a command device. The commanddevice interface 601 is composed of a control parameter, an inputparameter, and edited data. The control parameter is composed of a“process number” that indicates a command to be executed by a relevantstorage device, and a “presence or absence of edited data” thatindicates whether or not data is outputted as a result of the executionof the command. The input parameter sets parameter information that isused when executing the command. Also, the edited data sets data that isoutputted as a result of executing the command.

An outline of a process flow to execute a command using a command devicewill be described with reference to FIG. 7. The information processingdevice 11 is equipped with a command setting section 701 and a commandtransmission section 702. The command setting section 701 generates datathat sets in a command interface 601 a “process number” of a command tobe executed by the first storage device 10 and its “presence or absenceof edited data.” The command transmission section 702 transmits to thefirst write request section 401 a request to write the data in a firstlogical volume, which is a command device of the first storage device10, according to a first communications protocol.

The first storage device 10 is equipped with a command execution section703. The command execution section 703 is equipped with a pairmanagement section 704, a copy forming section 705, a restore section706, a journal storing section 707, a journal acquisition section 708and a journal stop section 709, which control pairs of the logicalvolumes 209 to be described below.

The command execution section 703 refers to a command device managementtable 501, and obtains a LUN of a command device that corresponds to thefirst storage device 10 (S701). The command execution section 703 refersto the command device (S702) and, if data in the form of the commanddevice interface 601 exists, executes a command designated by a processnumber indicated in the data.

Referring to flow charts in FIGS. 8 and 9, processes executed by theinformation processing device 11 and the storage devices 10 and 20 willbe described. First, the information processing device 11 sets a“process number” and a “presence or absence of edited data” in firstdata in the form of the command device interface 601 (S801). Then, theinformation processing device 11 refers to a command device managementtable 501 stored in the storage device 10, and obtains a LUN of arelevant command device of a storage device which executes the command.In order to write the created first data at the LUN obtained, theinformation processing device 11 transmits to the storage device 10 awrite request designating the LUN (S802).

Upon receiving the write request, the storage device 10 writes the firstdata in the command device at the designated LUN.

It is noted that command devices are logical devices that are defined onstorage areas of a plurality of storage devices, like the logicalvolumes 209, and write requests to the command devices are transmittedbased on the same communications protocol as that for write requeststransmitted to the logical volumes 209.

The storage device 10 refers to the command device management table 501,to specify LUNs of command devices that the storage device 10 itselfshould refers to, and monitors whether or not the command devices havedata written therein (S901). When the first data is found written in anyof the command devices under observation, the storage device 10 executesthe command designated by the process number in the first data (S902).Having completed the execution of the command, the storage device 10confirms whether edited data of the first data is present or absent(S903). When edited data is absent, the storage device 10 deletes thefirst data from the command device (S906). When edited data is present,the storage device 10 sets data outputted as a result of execution ofthe command as edited data (S904).

The information processing device 11 confirms whether edited data forthe command is present or absent (S803); and transmits to the storagedevice 10 a read request to read the edited data of the first data whenthe edited data is present (S804). Upon receiving the edited data fromthe storage device 10 (Yes at S805), the information processing device11 completes the processing. It is noted that the read request istransmitted based on the same communications protocol for read requestsfor the logical volumes 209 other than the command device.

When the edited data exists, after receiving the read request for theedited data from the information processing device 11 (S905), thestorage device 10 deletes the first data from the command device (S906).

In this manner, read or write requests that are used by the informationprocessing device 11 for reading or writing data from and to ordinarylogical volumes of the storage device 10, the information processingdevice 11 can transfer commands to the storage device 10.

Also, by using the virtual volumes, the information processing device 11can transfer commands to the second storage device 20 through the firststorage device 10, such that the second storage device 20 can executethe commands.

It is noted that, when the information processing device 11 requests thestorage device 10 and 20 to execute a “pair formation,” “journalacquisition,” “acquisition of processing state of journal,” “restore” or“swap” processing to be described below, the information processingdevice 11 uses the virtual volumes and command devices.

[Pair Formation]

Next, a description will be made as to a method for storing a copy ofdata in the logical volume 209 of the first storage device 10 in thelogical volume 209 of the second storage device 20.

FIG. 10 shows a pair management table 1001. In the pair management table1001, a column of “COPY SOURCE DEVICE” indicates storage devices (10 or20) to which those of the logical volumes of copy sources belong(hereafter referred to as “primary volumes”). A column of “COPYDESTINATION DEVICE” indicates storage devices (10 or 20) to which thoseof the logical volumes of copy destinations belong (hereafter referredto as “auxiliary volumes”). Also, a column of “PRIMARY LUN” indicatesLUNs of the corresponding primary volumes, and a column of “AUXILIARYLUN” indicates LUNs of the corresponding auxiliary volumes. Eachcorrespondence between a primary volume and an auxiliary volume iscalled a “pair.” Those of the logical volumes 209 for storing journals(to be described below) are assigned to the primary volumes andauxiliary volumes. A column of “PRIMARY JOURNAL LUN” sets LUNs of thelogical volumes 209 of the journals assigned for the primary volumes(hereafter referred to as “primary journals”). A column of “AUXILIARYJOURNAL LUN” sets LUNs of the logical volumes 209 of the journalsassigned for the auxiliary volumes (hereafter referred to as “auxiliaryjournals”).

Any one of appropriate methods for assigning the logical volumes 209 forstoring the journals can be used. For example, the user himself/herselfmay designate those of the logical volumes 209 to be used as thejournals, or the information processing device 11 may select appropriateunused ones of the logical volumes 209.

Referring to FIG. 11, an example of a process flow in forming pairs willbe described. In this example, it is assumed that the first storagedevice 10 is equipped with a third logical volume and a fifth logicalvolume, and the second storage device 20 is equipped with a fourthlogical volume and a sixth logical volume. The information processingdevice 11 transmits a command to the first storage device 10 and thesecond storage device 20 for forming a pair of the third logical volumeas being a primary volume 1101 and the fourth logical volume as being anauxiliary volume 1102, and a pair of the fifth logical volume as being aprimary journal 1103 and the sixth logical volume as being an auxiliaryjournal 1104 (S1101, S1102). The pair management sections 704 of thefirst and second storage devices 10 and 20 store information indicatingthe states of the pairs in the pair management tables 1001 of therespective storage devices 10 and 20. The copy forming section 705 ofthe second storage device 20 transmits to the first storage device 10 aread request to read data in the primary volume; and upon receiving fromthe first storage device 10 a copy of the data in the primary volume,the second storage device 20 writes the data in the auxiliary volume(S1103). By this operation, the data in the primary volume and the datain the auxiliary volume can be matched with each other. A processingthat brings the primary volume in conformity with the auxiliary volumeby a pair forming instruction is called an “initial copy” processing.

Also, the journal storage section 707 of the first storage device 10starts a processing to obtain a copy of the data written in the primaryvolume and its positional information in the primary journal. Thecorrelation between the primary volume and the primary journal isdescribed hereunder with reference to FIG. 12. The primary journal iscomposed of a meta data region 1201 and a journal data region 1202. Thejournal storage section 707 of the first storage device 10 stores a copyof the data written in the primary volume (hereafter referred to as“journal data”) in the journal data region 1202. Also, the journalstorage section 707 of the first storage device 10 stores in the metadata region 1201 the time when data 1203 is updated in the primaryvolume, LBA(s) 1204 of the data 1203, LBA(s) 1206 of the correspondingjournal data region, and the data 1203, LBA(s) 1205 of the journal data1206 in the corresponding journal data region, and the data length ofthe updated data. Also, the auxiliary journal is composed of a meta dataregion 1201 and a journal data region 1202 like the primary journal.

logical volume 209 of the second storage device 20 can be stored in thelogical volume 209 of the first storage device 10 by an instruction fromthe information processing device 11.

As a result, without performing data communications between pluralinformation processing devices, and without adding new commands to theoperating system of the information processing device 11, data stored ina storage device at a primary site can be stored as a backup in astorage device at a remote site. Also, in accordance with the presentembodiment, a storage device at a remote site transmits a read requestto a storage device at a primary site to thereby perform a copy formingprocessing. By this, the processing load on the storage device at theprimary site during the copy forming processing is alleviated. In otherwords, in a method in which a storage device at a primary site writesdata in a storage device at a remote site, the storage device at theprimary site needs to write the data in the storage device at the remotesite after it to confirms that the storage device at the remote site isready for forming a pair. For this reason, the processing load on thestorage device at the primary site becomes heavier, which would affectthe overall performance of the primary site that is performing otherprimary processings. In contrast, in accordance with the presentembodiment, since the storage device at the primary site only has tosend data in response to a read request from the storage device at theremote site, the processing load at the storage device at the primarysite can be alleviated.

[Restoration]

Even after the copy forming processing is performed, the first storagedevice 10 accepts write requests from the information processing device11, and updates the data in the primary volumes. For this reason, thedata in the primary volumes becomes inconsistent with the data in theauxiliary volumes. As described above, the primary journal storesjournal data for executions performed even after the copy formingprocessing took place. In this respect, the second storage device 20copies data stored in the primary journal into the auxiliary journal,and writes the data stored in the auxiliary journal into the auxiliaryvolumes, such that updates of the data on the primary volumes can belikewise performed on the auxiliary volumes.

Here, a processing to copy data stored in the primary journal into theauxiliary journal by the second storage device 20 is referred to as a“journal acquisition” processing, and a processing to write journal datastored in the auxiliary journal into the auxiliary volume is referred toas a “restoration” processing.

FIG. 13 shows a flowchart of the journal acquisition processing. Theinformation processing device 11 transmits a journal acquisitioninstruction to the second storage device 20 (S1301). Upon receiving thejournal acquisition instruction, the journal acquisition section 708 ofthe second storage device 20 refers to the pair management table 1001,and obtains a primary journal LUN of the corresponding pair. The journalacquisition section 708 of the second storage device 20 transmits to thefirst storage device 10 a read request to read the primary journal. Uponreceiving a copy of data of the primary journal, the journal acquisitionsection 708 of the second storage device 20 writes the data in theauxiliary journal (S1302).

Next, referring to FIG. 14, a processing flow of a restorationprocessing will be described. The information processing device 11transmits to the second storage device 20 a restore instruction torestore data in the auxiliary journal onto the auxiliary volumes(S1401). Upon receiving the restore instruction, the restore section 706of the second storage device 20 writes journal data stored in theauxiliary journal into the auxiliary volumes.

FIG. 15 shows journal data regions 1202 for the primary journal and theauxiliary journal. The journal data regions for the primary journal andthe auxiliary journal are defined by the same head LBA and end LBA,respectively. The journal data region 1202 for the primary journal iscomposed of journal storage completed regions 1502, 1503 and 1504 whichstore journal data, and purge completed regions 1501 which do not storejournal data.

The journal data region 1202 of the auxiliary journal is composed ofrestoration completed regions 1521 that store journal data that havealready been used for restoration in the auxiliary volumes, restorein-progress region 1522 that stores journal data that are designated forrestoration, read completed region 1523 that stores journal data thatare not designated for restoration, and read in-progress region 1524that stores journal data that are being read from the primary journal inresponse to a journal acquisition instruction.

Each of the storage devices 10 and 20 stores journal data in the journaldata region 1202 from the head LBA to the end LBA in a chronologicalorder as the journal data is created. When the journal data reaches theend LBA, each of the storage devices 10 and 20 returns to the head LBAagain, and stores journal data from there. In other words, the storagedevices 10 and 20 use the journal data regions cyclically between thehead LBA and the end LBA.

The first storage device 10 that is equipped with the primary journalstores a journal-out LBA 1511 which is a head LBA of the journal storagecompleted regions 1502, 1503 and 1504, and a journal-in LBA 1512 whichis a head LBA of the purge completed region 1501. When the journal outLBA and the journal-in LBA are equal to each other, it means thatjournal data is not stored in the primary journal.

The second storage device 20 that is equipped with the auxiliary journalstores a restoration completed LBA 1531 which is the highest LBA of therestoration completed region 1521, a to-be restored LBA 1532 which isthe highest LBA of the restore in-progress region 1522, a read completedLBA 1533 which is the highest LBA of the read completed region 1523, anda to-be read LBA 1534 which is the highest LBA of the read in-progressregion 1524.

In other words, when the restoration completed LBA 1531 and the to-berestored LBA 1532 are equal to each other, it means that a restorationprocessing instructed by the information processing device 11 has beencompleted. Also, when the read completed LBA 1533 and the to-be read LBA1534 are equal to each other, it means that a journal acquisitionprocessing instructed by the information processing device 10 has beencompleted.

The information processing device 11 can transmit to the first storagedevice 10 and the second storage device 20 a request to obtain theprocessing state of journal. Each of the storage devices 10 and 20confirms the states of LBAs that indicate the boundaries of the regionsdescribed above, and responds to the request.

Also, since the storage devices 10 and 20 use the journal data regionscyclically as described above, regions that become unnecessary need tobe released. The processing to release a region is called a “purge”processing. Each of the storage devices 10 and 20 can perform a purgeprocessing by changing addresses of LBAs that indicate the boundaries ofthe regions. The first storage device 10 can purge the journal storagecompleted region 1502, among the journal storage completed regions 1502,1503 and 1504 of the primary journal, which the second storage device 20has completed acquiring the journal data into the auxiliary journal. Inthis case, the first storage device 10 changes the journal-out LBA 1511to the head LBA of the journal storage completed region 1503, such thatthe journal storage completed region 1502 becomes the purge completedregion 1501. The second storage device 20 treats the restorationcompleted region 1521 of the auxiliary journal as a region that ispurged, and stores the journal data obtained in response to the journalacquisition instruction in the restoration completed region 1521.

Referring to a flowchart in FIG. 16, flows of the journal acquisitionprocessing and the restoration processing will be described. Theinformation processing device 11 transmits to the first storage device10 a request to obtain the processing status of the primary journal(S1601). The information processing device 11 transmits to the firststorage device 10 a read request to read edited data of a command deviceat which the processing status of the primary journal is set (S1602).Upon receiving the edited data of the command device from the firststorage device 10 (S1603), the information processing device 11transmits to the second storage device 20 a journal acquisition requestto obtain journal data starting at the journal-out LBA 1511 to a LBAimmediately before the journal-in LBA 1512 (S1604). The informationprocessing device 11 transmits to the second storage device 20 a requestto obtain the processing status of the auxiliary journal (S1605). Theinformation processing device 11 transmits to the second storage device20 a read request to read edited data of a command device at which theprocessing status of the auxiliary journal is set (S1606). Uponreceiving the edited data of the command device from the second storagedevice 20 (S1607), the information processing device 11 compares theread completed LBA 1533 and the to-be read LBA 1534 set in the editeddata, to confirm whether or not acquisition of the journal data has beencompleted (S1608). When the acquisition of the journal data has beencompleted, the information processing device 11 transmits to the secondstorage device 20 a restore request to restore journal data up to theread completed LBA 1533 (S1609). Then, the information processing device11 transmits to the first storage device 10 a purge request to purge thejournal data up to the read completed LBA 1533 (S1610). The informationprocessing device 11 repeats the journal acquisition processing andrestoration processing.

By the processings described above, updated data in a storage device ata primary site can be reflected on a storage device at a remote sitewithout performing data communications between multiple informationprocessing devices, and without adding new commands to the operatingsystem of the information processing devices. It is noted that, with aninstruction from the information processing device 11 that iscommunicatively connected to a storage device at a remote site, thestorage device at the remote site can obtain journal data from a storagedevice at a primary site and restore the data.

[Swap]

Let us assume that a primary volume of the first storage device 10 andan auxiliary volume of the second storage device 20 form a pair by aninstruction from an information processing device 11 (hereafter referredto as a “first information processing device”) that is communicativelyconnected to the first storage device 10. In this case, if a failureoccurs in the first information processing device 10, an informationprocessing device 11 (hereafter referred to as a “second informationprocessing device”) that is communicatively connected to the secondstorage device 20 can continue processings that have been performed bythe first information processing device, using the auxiliary volume ofthe pair. In this instance, the second information processing deviceswitches the relation between the primary volume and the auxiliaryvolume. In other words, a pair is formed with the logical volume 209 ofthe second storage device 20 being a primary volume and the logicalvolume 209 of the first storage device 10 being an auxiliary volume.Such a processing to switch the pair relation is called a “swap”processing.

Referring to FIGS. 17 and 18, a flow of processings to swap a pair willbe described. As shown in FIG. 17, the second information processingdevice 11 transmits a pair swap instruction to the first storage device10 and the second storage device 20 (S1701, S1702). Upon receiving thepair swap instruction, the journal stop section of the first storagedevice 10 stops storing journals in the primary volume. Also, the pairmanagement section 704 of the first storage device 10 swaps the primaryvolume and the auxiliary volume registered in the pair management table1001. Similarly, the pair management section 704 of the second storagedevice 20 swaps the primary volume and the auxiliary volume registeredin the pair management table 1001. The journal storage section 707 ofthe second storage device 20 starts storing journals of the logicalvolume 209 of the second storage device 20, which defines the primaryvolume.

FIG. 18 shows a state in which a pair is formed with the logical volume209 of the second storage device 20 being the primary volume and thelogical volume 209 of the first storage device 10 being the auxiliaryvolume, as a result of the swap processing performed by the firststorage device 10 and the second storage device 20 which received thepair swap instruction.

The swap processing performed by the second information processingdevice 20 and the storage devices 10 and 20 will be described in detailwith reference to flowcharts in FIGS. 19 through 21. The secondinformation processing device executes the journal acquisitionprocessing and the restoration processing described above (S1901). Thesecond information processing device transmits to the second storagedevice 20 a request to obtain the processing status of the auxiliaryjournal (S1902). The second information processing device transmits tothe second storage device 20 a read request to read edited data of acommand device in which the processing status of the auxiliary journalis set (S1903). Upon receiving the edited data of the command devicefrom the second storage device 20 (S1904), the second informationprocessing device compares the restoration completed LBA 1531 and theto-be restored LBA 1532 set in the edited data, to confirm if therestoration processing has been completed (S1905). If the restorationhas been completed, the second information processing device transmits apair swap request to the first storage device 10 and the second storagedevice 20 (S1906, S1907). Upon receiving the pair swap request, thefirst storage device 10 stops its journal acquisition processing withrespect to the primary volume (S2001), and swaps the relation betweenthe copy source and the copy destination registered in the pairmanagement table 1001 (S2002). Also, the second storage device 20, thathas received the pair swap request, swaps the relation between the copysource and the copy destination registered in the pair management table1001 (S2101), and starts a journal acquisition processing with respectto the primary volume of the second storage device 20 (S2102).

Let us consider as an example an information processing system that iscomposed of a primary site and a remote site. The primary site isequipped with a first information processing device and a first storagedevice 10, and the remote site is equipped with a second informationprocessing device and a second storage device 20. When a failure occursin the first information processing device, the second informationprocessing device uses the second storage device 20 to continue primaryprocessings performed at the primary site. The second informationprocessing device may instruct the first storage device 10 and thesecond storage device 20 to execute the swap instruction describedabove, such that the second storage device 20 is used for the primaryprocessings, and data on the second storage device 20 can be stored as abackup in the first storage device 10. Furthermore, since the data onthe second storage device 20 is stored as a backup in the first storagedevice 10, the execution of the primary processings can be quicklyswitched to the primary site, when the first information processingdevice is recovered from the failure.

Also, since the pair swap instructions from the information processingdevice 11 to the storage devices 10 and 20 are provided using read/writecommands with which the information processing device 11 is equipped,there is no need to add new commands to the operating system on theinformation processing device 11.

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof. The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims, rather than theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

1. A method for controlling a storage device system, the storage devicesystem including: an information processing device, a first storagedevice equipped with a first storage volume, and a second storage deviceequipped with a second storage volume, wherein the informationprocessing device and the first storage device are communicativelyconnected to one another, the first storage device and the secondstorage device are communicatively connected to one another, theinformation processing device is equipped with a first write requestsection that requests to write data in the first storage deviceaccording to a first communications protocol, and the first storagedevice is equipped with a second write request section that requests towrite data in the second storage device according to a secondcommunications protocol, the method comprising: a step conducted by theinformation processing device of creating first data including a firstinstruction to be executed in the second storage device; a stepconducted by the information processing device of transmitting to thefirst write request section a request to write the first data in thefirst storage volume according to the first communications protocol; astep conducted by the first storage device of, when the first datawritten in the first storage volume is an instruction to the secondstorage device, transmitting to the second write request section arequest to write the first data in the second storage volume accordingto the second communications protocol; a step conducted by the secondstorage device of executing the first instruction set in the first datawritten in the second storage volume; a step conducted by theinformation processing device of creating second data including a secondinstruction to be executed by the first storage device; a step conductedby the information processing device of transmitting to the first writerequest section a request to write the second data in the first storagevolume according to the first communications protocol; and a stepconducted by the first storage device of, when the second data writtenin the first storage volume is an instruction to the first storagedevice, executing the second instruction.
 2. A method for controlling astorage device system according to claim 1, wherein the first storagedevice includes a third storage volume, the second storage deviceincludes a fourth storage volume, and the second storage device includesa read request section that requests the first storage device to readdata according to a third communications protocol, the method furthercomprising: a step conducted by the information processing device ofcreating the first data including as the first instruction a pairforming instruction to form a pair of the third storage volume as beinga primary storage volume and the fourth storage volume as being anauxiliary storage volume; and a step conducted by the second storagedevice of receiving the pair forming instruction set in the first datawritten in the second storage volume, and transmitting to the readrequest section a request to read data in the third storage volume andwrite the data into the fourth storage volume according to the thirdcommunications protocol.
 3. A method for controlling a storage devicesystem according to claim 2, wherein the first storage device includes afifth storage volume, and the second storage device includes a sixthstorage volume, wherein a pair is formed with the third storage volumeas being a primary storage volume and the fourth storage volume as beingan auxiliary storage volume, and a copy of data to be written in thethird storage volume and positional information of the data are storedin the fifth storage volume as a journal, the method further comprising:a step conducted by the information processing device of creating thefirst data including as the first instruction a journal acquisitioninstruction to store a copy of the journal into the sixth storagevolume; and a step conducted by the second storage device of receivingthe journal acquisition instruction set in the first data written in thesecond storage volume, and transmitting to the read request section arequest to read data in the fifth storage volume and write the data intothe sixth storage volume according to the third communications protocol.4. A method for controlling a storage device system according to claim3, further comprising: a step conducted by the information processingdevice of creating the first data including as the first instruction arestoration instruction to update the fourth storage volume using ajournal stored in the sixth storage volume; and a step conducted by thesecond storage device of receiving the restoration instruction set inthe first data written in the second storage volume, and writing datastored in the journal written in the sixth storage volume into thefourth storage volume.
 5. A method for controlling a storage devicesystem according to claim 1, wherein the first storage includes a thirdstorage volume, and the second storage device includes a fourth storagevolume and a sixth storage volume, the method further comprising: a stepconducted by the information processing device of creating the firstdata including as the first instruction a pair forming instruction toform a pair of the third storage volume as being an auxiliary storagevolume and the fourth storage volume as being a primary storage volume;and a step conducted by the second storage device of receiving the pairforming instruction set in the first data written in the second storagevolume, and storing in the sixth storage volume a copy of data to bewritten in the fourth storage volume and positional information of thedata as a journal.
 6. A method for controlling a storage device systemaccording to claim 5, further comprising a step conducted by the secondstorage device of storing pair management information indicating thatthe pair is formed with the third storage volume as being an auxiliarystorage volume and the fourth storage volume as being a primary storagevolume.
 7. A method for controlling a storage device system according toclaim 6, further comprising: a step conducted by the informationprocessing device of creating the first data including as the firstinstruction a pair swap instruction to swap the pair such that the thirdstorage volume is set as a primary storage volume and the fourth storagevolume is set as an auxiliary storage volume; a step conducted by thesecond storage device of receiving the pair swap instruction set in thefirst data written in the second storage volume, and storing in the pairmanagement information data indicating that the third storage volume isthe primary storage volume and the fourth storage volume is theauxiliary storage volume; and a step conducted by the second storagedevice of receiving the pair swap instruction, and stopping the step ofstoring in the sixth storage volume history of data written in thefourth storage volume as a journal.
 8. A storage device systemcomprising: an information processing device; a first storage deviceequipped with a first storage volume; and a second storage deviceequipped with a second storage volume wherein the information processingdevice and the first storage device are communicatively connected to oneanother, the first storage device and the second storage device arecommunicatively connected to one another, the information processingdevice is equipped with a first write request section that requests towrite data in the first storage device according to a firstcommunications protocol, the first storage device is equipped with asecond write request section that requests to write data in the secondstorage device according to a second communications protocol, theinformation processing device is equipped with an instruction settingsection that creates first data including a first instruction to beexecuted in the second storage device, and an instruction transmissionsection that transmits to the first write request section a request towrite the first data in the first storage volume according to the firstcommunications protocol, the first storage device is equipped with adata transfer section that, when the first data written in the firststorage volume is an instruction to the second storage device, transmitsto the second write request section a request to write the first data inthe second storage volume according to the second communicationsprotocol, and the second storage device is equipped with an instructionexecution section that executes the first instruction set in the firstdata written in the second storage volume, and wherein the informationprocessing device is equipped with the instruction setting section thatcreates second data including a second instruction to be executed by thefirst storage device, the information processing device is equipped withthe instruction transmission section that transmits to the first writerequest section a request to write the second data in the first storagevolume according to the first communications protocol, and the firststorage device is equipped with a first instruction execution sectionthat, when the second data written in the first storage volume is aninstruction to the first storage device, executes the secondinstruction.
 9. A storage device system according to claim 8, whereinthe first storage device is equipped with a third storage volume, thesecond storage device is equipped with a fourth storage volume, thesecond storage device is equipped with a read request section thatrequests the first storage device to read data according to a thirdcommunications protocol, the information processing device is equippedwith the instruction setting section that creates the first dataincluding as the first instruction a pair forming instruction to form apair of the third storage volume as being a primary storage volume andthe fourth storage volume as being an auxiliary storage volume, and thesecond storage device is equipped with a copy forming section thatreceives the pair forming instruction set in the first data written inthe second storage volume, and transmits to the read request section arequest to read data in the third storage volume and write the data intothe fourth storage volume according to the third communicationsprotocol.
 10. A storage device system according to claim 9, wherein thefirst storage device is equipped with a fifth storage volume, the secondstorage device is equipped with a sixth storage volume, wherein a pairis formed with the third storage volume as being a primary storagevolume and the fourth storage volume as being an auxiliary storagevolume, and a copy of data to be written in the third storage volume andpositional information of the data are stored in the fifth storagevolume as a journal, the information processing device is equipped withthe instruction setting section that creates the first data including asthe first instruction a journal acquisition instruction to store a copyof the journal into the sixth storage volume, and the second instructionexecution section is equipped with a journal acquisition section thatreceives the journal acquisition instruction set in the first datawritten in the second storage volume, and transmits to the read requestsection a request to read data in the fifth storage volume and write thedata into the sixth storage volume according to the third communicationsprotocol.
 11. A storage device system according to claim 10, wherein theinformation processing device is equipped with the instruction settingsection that creates the first data including as the first instruction arestoration instruction to update the fourth storage volume using ajournal stored in the sixth storage volume, and the second instructionexecution section is equipped with a restoration section that receivesthe restoration instruction set in the first data written in the secondstorage volume, and writes data stored in the journal written in thesixth storage volume into the fourth storage volume.
 12. A storagedevice system according to claim 8, wherein the first storage isequipped with a third storage volume, the second storage device isequipped with a fourth storage volume and a sixth storage volume, theinformation processing device is equipped with the instruction settingsection that creates the first data including as the first instruction apair forming instruction to form a pair of the third storage volume asbeing an auxiliary storage volume and the fourth storage volume as beinga primary storage volume, and the second storage device is equipped witha journal storage section that receives the pair forming instruction setin the first data written in the second storage volume, and stores inthe sixth storage volume a copy of data written in the fourth storagevolume and positional information of the data as a journal.
 13. Astorage device system according to claim 12, wherein the second storagedevice is equipped with a pair management section that stores pairmanagement information indicating that the pair is formed with the thirdstorage volume as being an auxiliary storage volume and the fourthstorage volume as being a primary storage volume.
 14. A storage devicesystem according to claim 13, wherein the information processing deviceis equipped with the instruction setting section that creates the firstdata including as the first instruction a pair swap instruction to swapthe pair such that the third storage volume is set as a primary storagevolume and the fourth storage volume is set as an auxiliary storagevolume, the second instruction execution section is equipped with thepair management section that receives the pair swap instruction set inthe first data written in the second storage volume, and stores in thepair management information data indicating that the third storagevolume is the primary storage volume and the fourth storage volume isthe auxiliary storage volume, and the second storage device is equippedwith a journal stop section that receives the pair swap instruction, andstops a processing to store in the sixth storage volume history of datawritten in the fourth storage volume as a journal.
 15. A method forcontrolling a storage device system, the storage device systemincluding: an information processing device, a first storage deviceequipped with a first storage volume, and a second storage deviceequipped with a second storage volume, wherein the informationprocessing device is equipped with a first write request section thatrequests to write data in the first storage device according to a firstcommunications protocol, and the first storage device is equipped with asecond write request section that requests to write data in the secondstorage device according to a second communications protocol, the methodcomprising: a step of creating first data including a first instructionto be executed by the second storage device; a step of transmitting tothe first write request section a request to write the first data in thefirst storage volume according to the first communications protocol; astep of, when the first data written in the first storage volume is aninstruction to the second storage device, transmitting to the secondwrite request section a request to write the first data in the secondstorage volume according to the second communications protocol; a stepof executing the first instruction set in the first data written in thesecond storage volume; a step of creating second data including a secondinstruction to be executed by the first storage device; a step oftransmitting to the first write request section a request to write thesecond data in the first storage volume according to the firstcommunications protocol; and a step of, when the second data written inthe first storage volume is an instruction to the first storage device,executing the second instruction.
 16. A method for controlling a storagedevice system according to claim 15, wherein the first storage deviceincludes a third storage volume, the second storage device includes afourth storage volume, and the second storage device includes a readrequest section that requests the first storage device to read dataaccording to a third communications protocol, the method furthercomprising: a step of creating the first data including as the firstinstruction a pair forming instruction to form a pair of the thirdstorage volume as being a primary storage volume and the fourth storagevolume as being an auxiliary storage volume; and a step of receiving thepair forming instruction set in the first data written in the secondstorage volume, and transmitting to the read request section of thesecond storage device a request to read data from the third storagevolume and write the data in the fourth storage volume according to thethird communications protocol.
 17. A method for controlling a storagedevice system according to claim 16, wherein the first storage deviceincludes a fifth storage volume, and the second storage device includesa sixth storage volume, wherein a pair is formed with the third storagevolume as being a primary storage volume and the fourth storage volumeas being an auxiliary storage volume, and a copy of data to be writtenin the third storage volume and positional information of the data arestored in the fifth storage volume as a journal, the method furthercomprising: a step of creating the first data including as the firstinstruction a journal acquisition instruction to store a copy of thejournal into the sixth storage volume; and a step of receiving thejournal acquisition instruction set in the first data written in thesecond storage volume, and transmitting to the read request section ofthe second storage device a request to read data in the fifth storagevolume and write the data in the sixth storage volume according to thethird communications protocol.
 18. A method for controlling a storagedevice system according to claim 17, further comprising: a step ofcreating the first data including as the first instruction a restorationinstruction to update the fourth storage volume using a journal storedin the sixth storage volume; and a step of receiving the restorationinstruction set in the first data written in the second storage volume,and writing data stored in the journal written in the sixth storagevolume into the fourth storage volume.
 19. A method for controlling astorage device system according to claim 15, wherein the first storageincludes a third storage volume, and the second storage device includesa fourth storage volume and a sixth storage volume, the method furthercomprising: a step of creating the first data including as the firstinstruction a pair forming instruction to form a pair of the thirdstorage volume as being an auxiliary storage volume and the fourthstorage volume as being a primary storage volume; and a step ofreceiving the pair forming instruction set in the first data written inthe second storage volume, and storing in the sixth storage volume acopy of data to be written in the fourth storage volume and positionalinformation of the data as a journal.
 20. A method for controlling astorage device system according to claim 19, further comprising a stepof storing pair management information indicating that the pair isformed with the third storage volume as being an auxiliary storagevolume and the fourth storage volume as being a primary storage volume.21. A method for controlling a storage device system according to claim20, further comprising: a step of creating the first data including asthe first instruction a pair swap instruction to swap the pair such thatthe third storage volume is set as a primary storage volume and thefourth storage volume is set as an auxiliary storage volume; a step ofreceiving the pair swap instruction set in the first data written in thesecond storage volume, and storing in the pair management informationdata indicating that the third storage volume is the primary storagevolume and the fourth storage volume is the auxiliary storage volume;and a step of receiving the pair swap instruction, and stopping the stepof storing in the sixth storage volume history of data written in thefourth storage volume as a journal.